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DovecotApplication

CVE-2026-27859

MEDIUM · 5.3 CVSS v3.1 Published 2026-03-27
Fix available
A fix is available. Upgrade to 2.4.3 / 3.0.5 or later.
See remediation →
62/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A mail message containing excessive amount of RFC 2231 MIME parameters causes LMTP to use too much CPU. A suitably formatted mail message causes mail delivery process to consume large amounts of CPU time. Use MTA capabilities to limit RFC 2231 MIME parameters in mail messages, or upgrade to fixed version where the processing is limited. No publicly available exploits are known.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

A vulnerability in LMTP (Local Mail Transfer Protocol) allows specially crafted mail messages containing excessive RFC 2231 MIME parameters to cause the mail delivery process to consume disproportionate CPU resources, resulting in potential denial of service. The issue stems from lack of input limits on MIME parameter parsing.

MitigationImplement RFC 2231 MIME parameter limits via MTA configuration, or upgrade to the vendor's patched version that includes built-in processing limits.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
DovecotApplication
Affected:< 2.4.3
DovecotApplication
Affected:< 3.0.5>= 3.1.0, < 3.1.4

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed Dovecot version
    Run 'dovecot --version' or check the package manager (e.g., 'rpm -q dovecot' or 'dpkg -l dovecot')
    Affected if The version is less than 2.4.3, or between 3.0.0 and 3.0.4, or between 3.1.0 and 3.1.3
  2. Confirm LMTP service is enabled
    Check dovecot configuration for 'protocol lmtp' in /etc/dovecot/conf.d/ or run 'dovecot -n' to see enabled protocols
    Affected if LMTP protocol is listed among enabled services in the Dovecot configuration
  3. Check if LMTP is actively listening or configured for mail delivery
    Look for 'service lmtp' entries in dovecot.conf or check if LMTP is bound to a socket or port used for local mail delivery
    Affected if LMTP is configured and active as a delivery agent for incoming mail
  4. Verify MTA integration with Dovecot LMTP
    Inspect MTA configuration (Postfix, Exim, or Sendmail) for 'lmtp' transport or socket paths pointing to Dovecot LMTP
    Affected if The MTA is configured to deliver mail via Dovecot LMTP, exposing the vulnerability to incoming messages

You are affected if Dovecot version is in the vulnerable range (<2.4.3, <3.0.5, or >=3.1.0 with <3.1.4) AND LMTP is enabled as a mail delivery protocol.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 2.4.3 / 3.0.5 / 3.1.4 or later
Fixed in 2.4.33.0.53.1.4
Interim mitigation

Implement RFC 2231 MIME parameter limits via MTA configuration, or upgrade to the vendor's patched version that includes built-in processing limits.

Recommended fix Moderate confidence

Dovecot 2.4.3 (for 2.x users), Dovecot 3.0.5 (for 3.0.x users), or Dovecot 3.1.4 (for 3.1.x users)

  1. 1. Identify the currently installed Dovecot version using: dovecot --version
  2. 2. Determine which release branch you are currently running (2.x, 3.0.x, or 3.1.x)
  3. 3. For Dovecot 2.x: Upgrade to version 2.4.3 or later
  4. 4. For Dovecot 3.0.x: Upgrade to version 3.0.5 or later
  5. 5. For Dovecot 3.1.x: Upgrade to version 3.1.4 or later
  6. 6. Use your system's package manager to perform the upgrade (e.g., apt-get update && apt-get install dovecot, or yum/dnf update dovecot)
  7. 7. After upgrade, verify the new version is installed: dovecot --version
  8. 8. Restart the Dovecot service to apply changes: systemctl restart dovecot or service dovecot restart
Caveat Standard upgrade risks apply - review Dovecot upgrade documentation for any configuration changes between your current version and the target fixed version, particularly when crossing major version boundaries (2.x to 3.x)

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Dovecot Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,240
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-27859 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data